Ovulation Calculator
Predict your most fertile days and ovulation date based on your menstrual cycle.
Enter Your Values
Enter your values and press Calculate: you will get the result, its method, the inputs used and confidence, plus copy, print and share options.
How this calculator works
ACOG pregnancy datingv1.0.0
Due-date estimation by LMP (Naegele), conception date, IVF transfer date, or ultrasound-established EDD.
- Applies to
- Pregnancies with regular dating information
- Assumptions
- Regular cycles for LMP mode (adjustable)
- Limitations
- Ultrasound in the first trimester is the most accurate dating method
- Output
- date / gestational age
- Last reviewed
- 2026-06-01
Evidence Sources & Literature
- American College of Obstetricians and Gynecologists. Committee Opinion 700: Methods for Estimating the Due Date. Obstet Gynecol, 2017. doi:10.1097/AOG.0000000000002056.
About the Ovulation Calculator
If you are trying to conceive (or trying to understand your cycle), knowing when you ovulate is genuinely powerful information, because it identifies the few days each month when pregnancy is possible. This calculator estimates your ovulation date and fertile window based on your cycle length and the start of your last period, giving you a practical timeline to work with.
I think understanding your own cycle is empowering whatever your goal. The calculator gives a solid estimate from your dates, and I will also share the body signs that can confirm ovulation more precisely, because combining the two gives you the clearest picture.
When ovulation happens
Ovulation is when an ovary releases an egg, and it typically occurs about 14 days before your next period starts. In a regular 28-day cycle that is around day 14, but the timing shifts with your cycle length: in a 30-day cycle it is closer to day 16, and in a 26-day cycle nearer day 12. The calculator uses your cycle length to estimate your ovulation day rather than assuming a standard cycle.
The fertile window
You are not only fertile on ovulation day itself. Because sperm can survive in the body for up to about five days, the fertile window spans roughly the five days before ovulation plus ovulation day, giving about six days when conception is possible. If you are trying to conceive, this whole window is what matters, not just a single day, which takes some of the pressure off precise timing.
Signs that confirm ovulation
Your body gives helpful clues. Cervical mucus tends to become clear, slippery and stretchy (like raw egg white) around ovulation. Basal body temperature rises slightly just after ovulation, so tracking it over a cycle reveals the pattern. Ovulation predictor kits detect the hormone surge that precedes ovulation. Combining these signs with the calculator's estimate pinpoints your fertile days far more reliably than a calendar alone, especially if your cycles are irregular.
When to seek support
Trying to conceive can take time even when everything is healthy; many couples conceive within a year of regular trying. If you are under 35 and have been trying for a year, or 35 and over and have been trying for six months, it is reasonable to talk with a healthcare provider. Irregular cycles or other concerns are also worth raising. This calculator is a helpful planning tool, and your provider is there for guidance and support along the way.
Dietitian Insight: Ovulation calculators project the fertile window by subtracting the typical 14-day luteal phase from cycle length. Learn about hormonal balance and fertile health, and map your cycle with our menstrual cycle tracker.
Sources & method
This calculator uses established, peer-reviewed formulas and reference ranges from recognized health and nutrition authorities. Results are estimates for general education, not a medical diagnosis. For decisions about your health, consult a qualified clinician. Reviewed by Macro & Meals Editorial Team, Content editor.
Frequently Asked Questions
When do I ovulate?
Ovulation typically occurs about 14 days before your next period. In a 28-day cycle that is around day 14, but it shifts with cycle length, closer to day 16 in a 30-day cycle and day 12 in a 26-day cycle. The calculator uses your cycle length to estimate your ovulation day.
What is the fertile window?
It is the roughly six days when conception is possible: the five days before ovulation, because sperm can survive that long, plus ovulation day itself. If you are trying to conceive, the whole window matters rather than a single day, which eases the pressure on precise timing.
How can I confirm when I ovulate?
Body signs help: cervical mucus becomes clear, slippery and stretchy around ovulation, basal body temperature rises slightly just after, and ovulation predictor kits detect the hormone surge beforehand. Combining these with the calculator's estimate pinpoints your fertile days more reliably, especially with irregular cycles.
How long should I try before seeing a doctor?
Many couples conceive within a year of regular trying. If you are under 35 and have been trying for a year, or 35 and over and trying for six months, it is reasonable to talk with a healthcare provider. Irregular cycles or other concerns are also worth raising sooner.
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